1. Field of the Invention
The present invention is directed to an electrode device intended to be at least partially implanted temporarily into living tissue.
2. Description of the Prior Art and Related Application
In general, medical electrode devices intended for implantation in a patient include an electrically insulating sheath, an electrical conductor contained in the insulating sheath, an electrode disposed on the insulating sheath, and in electrical contact with the conductor, and a contact disposed at proximal end of the insulating sheath and also in electrical contact with the conductor. The contact is adapted for electrical and mechanical connection to a medical apparatus which emits and/or receives electrical signals, which are carried by conductor. The electrode interacts with living tissue to either deliver a signal from the medical apparatus to the tissue, or to sense a signal from the living tissue and to supply it, via the conductor, to the medical apparatus.
An electrode device of this type is described in U.S. Pat. No. 3,915,174. This known electrode device can be implanted in a heart either temporarily or permanently in order to stimulate the heart and to sense electrical heart signals. The electrode device can be connected either to an extracorporeal apparatus, or to an implantable apparatus, such as a pacemaker.
The utilization of temporary electrode devices for sensing electrical signals in body tissue is very useful in conjunction with, for example, the diagnosis of illnesses and in determining the most appropriate treatment for a patient. When such determination could include, for example, an investigation of whether a patient should be provided with an implantable defibrillator.
For reception of usable values in the monitoring of electrical signals in living tissue, the electrode device must be connected to the tissue in a reliable manner. Many different ways are known to attach the electrode device to tissue. In general, these known fixing techniques employ either an active fixing means or a passive fixing means. When the electrode device is attached to the tissue it will, after only a relatively short period of time, become embedded in the tissue. As a result, the electrode device cannot be easily removed after the investigation has been completed. Because the electrode becomes firmly embedded in tissue, the tissue may be damaged when the electrode device is explanted. Explanting a temporary electrode device, moreover, requires surgery as a rule, thereby increasing the risk to the patient. A common recourse for minimizing trauma to tissue and risk to the patient is simply to leave the electrode device implanted in the patient. This solution, however, is not without risk, because the electrode device, if left in the body, may irritate and even damage other tissue.
In the case of purely mechanical implants, i.e., implants not involving the transmission of electrical signals, which are only needed temporarily in the body of a patient, resorbable materials are currently being used to a large degree. The resorbable material gradually dissolves in the body, ultimately disappearing completely, and is usually replaced by living tissue. The presence of an electrical conductor, however, is a problem in implants wherein electrical signals must be transmitted. No resorbable electrical conductors are currently known.
In co-pending U.S. application Ser. No. 08/226,337 ("Medical Electrode Device Having A Non-Gaseous Fluid Conductor," Hoegnelid et al., filed Apr. 12, 1994), an electrode device is disclosed wherein, instead of using a metallic conductor, a nongaseous fluid conductor is used in order to reduce the risk of conductor fracture and short-circuits between conductors. Various types of non-gaseous fluid conductors are described therein, one of which, for sensing signals from tissue, is a liquid conductor consisting of an electrolyte. The electrolyte may be sodium chloride and water, making it completely harmless to tissue.